Brick having low modulus rupture



Jung 1s, 1.948 A .R P. HEUER, I 2,443,424

BRICK HAVING LOW MODULUS RUPTURE- 4 Filed may 12, 1944 2 snets-sneet 1F119- 2- [argl ,74 kf 1713.3.

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luasell jearce lucr www: In@ 13M forneys June l5, 1948. R. P. HEUER2,443,424

` BRICK run/Ine Low Monunus nurrm Filed nay 12, 1944 2 sheets-sheet 2@and Invenlor.

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, Mt. vc. .Bnzmgrd Chrome .Bu medMa gnesic Russe ll Pearce Heuer 2Oeflcclion a1' Miclpan in .aaaz' 0 0 0 0 0 O 0 0 0 0 O 0 0 7 6 5 w. vs 20 w o m 9 Patented June 1S, 1948 BRICK HAVING LOW MODULUS RUPTURERussell Pearce Heuer, Villa Nova, Pa., aslignor to General ReiractorlesCompany, a corporation of Pennsylvania Application May 12, 1944, SerialNo. 535,360

16 Claims.

My invention relates to the manufacture of basic reiractories comprisingchrome ore and dead burned magnesite or periclase.

One purpose of my invention is to manufacture basic refractory brickhaving high resistance to spalling which are characterized 'by a lowmodulus of rupture or low crushingfstrength after heating to hightemperature.

A further purpose is to produce basic refractory brick which have a lowmodulus of rupture after being heated to high temperature by using amixture of chrome ore and magnesite having a novel distribution ofparticle size and weight ratio of chrome ore to magnesite whichaccomplishes this objective. v

A further purpose is to provide basic refractory brick having a higherresistance to,crush ing strains ibefore firing than after firing and anabnormally low modulus of rupture after burning. y

A further purpose is to increase the resistance to spalling and reducethe modulus of rupture in a burned basic refractory brick by the use ofdead burned magnesite and chrome ore, the magnesite in excess of thechrome ore, made up of relatively large particles and relatively smallparticles and omitting intermediate particles.

A further purpose is to use a brick which has a low modulus of ruptureor a low crushing strength and to protect it from crushing by suspendingit within a roof in which it is to be used.

A further purpose is to avoid spalling by weakening the brick and thenmake up for this weakening by suspending the brick from the roof insteadofsupporting them in the usual sprung arch roof. y

A further purpose is to provide a brick which is of low porosity and yetstrong enough to be handled and shipped, which has low volume shrinkagewhen heated to a high temperature range such as is found in open hearthsteel furnaces and which is resistant to iron oxide attack.

A further purpose is to provide a brick made of larger size chrome andmagnesite particles and small size chrome and magnesite particles,lacking in the intermediate particles, all in oxide form, preferablyusing also finely ground aluminous material such as bauxite.

2 A further purpose is to provide a. chrome and magnesite :brick havingrelatively large and relatively small particles of each and lacking theintermediate particle sizes, to add a small amount of temporary bondingmaterial such as sulphuric acid, magnesium chloride, magnesium sulphateor organic binders, etc. to increase the strength of the dried brickbefore ring, with the result that the brick can be used without kilnburning.

Afurther purpose is to form a brick having resistance to crushing strainhigher in its unfired condition than in its burned condition, totransport the brick while dry and unfired and fburn it in place and toseparately support the brick in position within the roof of the furnace.

In the manufacture of basic refractory brick intended primarily for usein the roof of an open' hearth steel furnace, a further purpose is totake advantage of suspended support for the roof brick to permit the useof brick of low modulus of rupture designed and eective to protectagainst spalling and which could not f be used in sprung arches becauseof the comlpressive stresses there.

In the manufacture of a basic refractory roofl brick for use primarilyin an open hearth steel furnace, a further purpose is to reduce spallingby reducing the modulus of rupture or crushing strength, thus making thebrick when burned unsuitable to use within a sprung arch and to 4 Figure1 is a diagrammatic view showing a brick intended for suspended arch usein a vertical side elevation, the lower edge of the brick being exposedto the fire.

Figure 2 is a diagrammatic View giving the length of the brick in orderthat there may be plotted upon it the temperature gradient within abrick when in roof service.

Figure 3 is a diagrammatic side elevation in part broken at the bottomto illustrate the behavior of the brick. y

Figure 4 is a fragmentary enlarged diagrammatic illustration showing twoadjacent laminae among those in Figure 3.

Figure 5 is a side elevation in which the eifect in Figure 4 has beenplotted in the laminae shown in Figure 3.

Figure 6 is a diagrammatic side elevation showing the action of spallingupon the brick.

Figure is a diagrammatic view containing curves plotted comparatively toindicate modulus of rupture along one dimension plotted againstdeflection at midspan plotted at right angles thereto.

Figure 8 is a fragmentary section of a suspended brick roof made of:bricks from materials such as are claimed herein. Y

In the drawings similar numerals indicate like parts.

For the construction of roofs for open hearth furnaces it is customaryto use silica brick. The roof is formed by springing an arch to span thefurnace from skewbacks located in the furnace sidewalls. Steel tie rodsapply a horizontal compressive force to the skewbacks and roof brick. Avertical component of force is thereby produced in the arch to supportit against the force of gravity. The compressive forcesacting on theroof brick are substantial and a desirable refractory for this useshould have a sufficiently high crushing strength to withstand theforces present.

Efforts have been made to build sprung arches in metallurgical furnacesfrom refractory brick other than silica. Trials have been made withbasic brick comprising chrome ore and/or magnesite ln sprung arches withindifferent results.

I have found thaty spelling is much more pronounced where the modulusofrupture is high and where the strength .to resist crushing is high andthat the spalllng is greatly reduced by reducing'the strength to resistcrushing. However this introduces difficulties in supporting the archbecause the relatively high compressions on the bricks necessary tosupport the customary sprung arch tend to destroy the brick and makesuch a sprung arch brick impractical. However, I have vfound that thebricks can still be used in furnace roofs if the type of the roof bechanged radically and in place of the ksprung arch the roof be formed ofsuspended bricks in accordance with the teachings of my United StatesPatent No. 2,304,170.

I have successfully used suspended basic brick reverberatory smeltingfurnaces. In this case the copper furnace was a continuous furnace andthe temperature changes in the roof were held to a minimum. However,when similar suspended roof bricks using conventional basic bricks madeof chrome ore and magnesite were used in basic open hearth steelfurnaces, the results were not comparable with those obtained in thecopper smelting furnaces. One reason for this was that the open hearthfurnace is an intermittent furnace and the temperature of the roofchanges substantially during each successive heat. The changingtemperature in the open hearth furnace causes the brick to fracture andspall off along planes which are parallel to the exposed face of thebrick and about 1" from the heated end. This spalling causes prematurefailure of the roof.

The reason for the poor operation when using -roofs for sprung silicabrick roofs in large copper existing basic brick in the open hearthsteel furnace will now be explained in connection with Figures l to 6.

In Figure 1 the lower face of the` brick represented by line I5 isexposed to the heat of the furnace, the vertical faces being protectedby adjacent brick. This lower (hot) face of the brick may show atemperature of 3000 F. at the time a finished heat of steel is tappedfrom the furnace.

A thermal gradient prevails along the longitudinal axis of the Abrick asshown by the line ab in Figure 2. After the furnace is tapped thefurnace doors are opened, the fuel'ls shut off and a large quantity' ofcold charge ispplaced in the furnace. As a result the hot face of thebrick is cooled rapidly and its temperature may fall,

1000 F. or more. The line cb in Figure 2 represents the new conditionschematically. Since the cooling is relatively rapid, most of thetemperature change is confined to the end of the brick. At some interiorpoint such as it there is relatively little loss in temperature.

After charging is finished the fuel is again supplied to the furnace andthe hot face of the brick rises in temperature until the gradient shownby the line ab is again established. This operating cycle is repeatedagain and again. The brick are subjected to repeated strains and finallyfractures develop and the hot faces of the brick spall off. The new hotfaces are subjected to a similar treatment and gradually the brick aredestroyed. y

Figure 3 may be used to show the mechanism whereby these spalling cracksdevelop,y In this figure the heated end of the brick shown in Figure 1is represented as being composed o' a number of elements of thickness Sacross the width of the brick. 'Ihe strips here represented have extent,let us say, from one side of the brick to the other a total of 2%".

If each element were free to act independently when the temperaturefalls from T1 to T2 the dimension S would decrease in amount equal toSa(T1-T2)-(where a is the cceiiicient of expansion). Figure 4 shows twoof these assumed elementson an enlarged scale and illustrates what theeffect of this change in the dimension would be if the elements actedindependently. In the actual brick, however, each element S is firmlyattached to its neighboring element throughout the lengths and widths ofthe elements.

In order to maintain this continuous structure theindividual elementsmust undergo strains in amount suiiicient to compensate for the changeSa(T1-T2). This is accomplished in two ways. Tensile stresses are set upacross the hot face of the brick which increase the thickness of/theindividual elements. In addition the adherence of each element to itsneighbor tends toconform the adjoining elements to each other. Thisconformation plus the tensile strain attempts to compensate forSa(T1-Tz). The assembly of the strained elements is illustrated inFigure 5.

The tensile stress acting across/the hot face may rise to avalue whichthe refractory material cannot stand, whereupon a crack will result atabout to the hot face, as shown at uinFigure 6. The deformation of theelements at the-edge of the brick may exceed the strain which therefractory is capable of withstandingwhereupon a crack such as i8 inFigure 6 will start and then gradually work across the brick. Crackssimilar to I8 and I9 are observed in actual practice. As

- ance is better.

a result of the cracks, portions such as 2l and 2i separate from thebrick and fall oil.' as spalls.

. Of the two types of cracks indicated the cracks cause shearingstresses and consequent cracking of the refractory. In basic roofs theseshear cracks are seldom observed. However, the effect of deformation ofthe brick elements, upon heating. supplements the destructivedeformation 6 data on commercial burned vchrome-niaiznesite brick ofthis type. The deformation of this brick is better than the twopreceding 4types although it still leaves much to be desired as far asdeformation is concerned.

I have found that it is possible to produce basic i brick having betterdeformation characteristics caused by cooling and may therefore causefailure more rapidly.

In order to increase the resistance of basic brick to spalling it isnecessary to increase the resistance of the brick to repeateddeformation.

I have been able greatly to increase the deformation obtainable in,basic bricks as a result of studies I have made on the behaviorof'various kinds of brick when subjected to modulus of rupture test's.

The apparatus for making this test is the standard equipment recommendedby the American Society for Testing Materials and described in thatsociety's publication Manual of A. S. T. M. Standards on RefractoryMaterials June 1943 on pages 65-66 under the A. S. T. M. designation0133-39. The test is therefore their standard test. A standard sizebrick, 9 x 41/2 x 2% is used. The brick' is first reheated to 1500 C.for 24 hours, then cooled to room temperature and subjected to the test.The sample brick is tested as a beam resting on two transverse bearingedges 7" apart. A load is applied to the 9"l x 4% face along a lineparallel to the two supports and equidistant between them. Thedeflection of the beam is measured in units of 0.00m inch at the placewhere the load is applied. The load is gradually increased until failureoccurs and the deflection is noted for various loads applied. Themodulus of rupture is calculated from the load required at failure bythe formula.

where:

R=modulus of rupture in pounds per square inch,

W=total load in pounds at. which the specimen failed,

Z=distance between the supports in inches,

b=width of the 'specimen in inches, and g d=depth of the specimen ininches.

For intermediate loads a similar fibre stress is calculated and thecorresponding values plotted against the deflection.

In Figure 7 curve 22 shows test data plotted for a conventional burnedchrome brick. The shape of this curve is typical of strong, hard burnedbasic brick. The modulus of rupture is high (797 pounds per square inch)and the deilection just before failure is very small (0.014").

Curve 23 represents a typical burned magnesite brick. Its deformation atfailure is greater than the burned chrome brick and its spalling resist-In recent years improved basic brick having still better spallingresistance than straight magnesite or chrome brick have been made frommixtures of about '75% chrome ore and 25% magnesite. Curve 2| representstest by the use of a novel method of distributing the particle sizes andthe weight ratio of chrome ore and magnesite in the mix. Two typicalrefractory bodies (Examples 1 and 2) were made in accordance with thepresent method and tested for modulus of rupture and deflection. Theresults are shown in curves 2l and 2l, Figure 7.

At the point of ultimate failure these new bodies show a deflection morethan 2 to 8 times greater than with the conventional refractoriesreferred to above. Comparative data are assembled in Table l.

Table 1 This greater deflection causes a vastly greater resistance tospalling with subsequent longer life of the refractory under operatingconditions. In Example 26 a maximum of deflection has been obtained bypurposely making the refractory weak and of low modulus of rupture. Thelower the strength of the brick the better it conforms to therequirements which are necessary for best spalling'resistance. y

In applying the new type of weak refractory commercially the limitationsof its strength must be specifically provided for and wherever possibleit is recommended to be used in suspended roof construction and insimilar mechanically supported parts of furnaces. Such a suspendedconstruction does not require the high physical strength which hasheretofore been considered a necessary property of a basic refractory.Thus by choosing a suitable mechanical construction I am able tosuccessfully utilize a vrefractory of low modulus of rupture and in sodoing I obtain a vast improvement in spalling resistance which has notbeen obtained heretofore with the conventional types of basic brick. y

The manufacture of a basic brick of minimum modulus of rupture afterreheating to l500 C. and subsequent cooling is not the simple problemthat it may seem to be. While many of the recent improvements in basicbrick manufacture are said to produce hard burned brick of unusuallyhigh strength by the use of specialhigh-temperature kilns, high forming.pressure and the use of selected particle sizes in the mix, it does notnecessarily follow that low modulus of rupture is easily obtained bymerely doing away with all or most of these recent developments.

In obtaining the low modulus of rupture other desirable properties ofthe brick must not be sacrificed. The refractory must be dense, i. e.,

- of low porosity and be strong enough to .be hanchrome ore and deadburned magnesite or periclase.

A suitable chrome ore is the refractory grade ore obtained from theMasinloc deposit on the island of Luzon, Philippine Islands. Chrome orefrom the Moa Bay district of Cuba is also satisfactory. Typical analysesfollow:

Other refractory ores higher in chromic oxide may also he used. The oremay be used in its raw or natural state or after calcining at hightemperature if desired.

The desired chrome ore is iirst jaw crusher and then passed through aconventional muller-type perforated-bottom dry pan to grind the ore forscreening and selection of certain desired particle sizes to be used inthe brick mix. Since a preponderant amount of the chrome ore is used inthe form of relatively coarse particles, the choice of the ore and themethod of grinding should be made such as to produce l a maximum ofcoarser particles and a minimum of finer particles in the first grindingoperation, otherwise a large amount of the chrome ore will be too smallin size for ultimate use and will therefore be rejected.

The ground product which passes through the perforated bottom of the drypanl is screened over suitable vibrating screens to obtain a productwhich passes substantially 100% through a W. S. Tyler standard screen of6 meshes per linear inch. Whatsoever oversize there may be is returnedfor further grinding in the dry pan and further screening. In order tominimize the production of too many small sized particles, it may bedesirable to pass the ore as it comes from the crusher over the firstscreen before it goes to the dry pan.

The ground chrome ore which passes the first screen is then passed overa second vibrating screen which is designed to. pass all particles whichare small enough to go through a W. S.

Tyler standard screen of 28 mesh per linear inch. The product whichfails to pass this screen is set aside for subsequent use as coarsechrome particles. Particles which pass 6 mesh and rest on 28 meshstandard screens are preferred.

The size of the openings of the rst screen may be increased to produceparticles which will only pass the equivalent Tyler standard screens ofmesh per linear inch. The size of the screen openings may alternativelybe decreased so that the screened particles will just pass a W. S. Tylerstandard screen of 8 or 10 mesh per linear inch The size of the openingsin the second screen in similar manner may be increasedso that theproduct will rest substantially all on W. S. Tyler screens of mesh orthe size of thev openings may be decreased so that the product will restsubstantially all on a mesh Tyler screen. The difference in the size ofthe openings in the first and second screen should be kept reasonablysmall so that the range in size of the coarse chrome particles is notexcessive. Thus screening combinations of 6 and 28 mesh,

Aassess?.

crushed in. a

5 and 20 mesh or l0 and 304 mesh are practical f selections designed togive desirable production and good costs. I prefer the 6 and 28 meshcombination for most uses but the other sizes may be used if desired.

In preparing the chosen `sizes commercially,

` using for example, the 6 and 28 mesh combinationl the .product willusually contain some particles whicl'uon laboratorytest, will pass a. 28mesh standard screen. Suchv product can be used but the amount ofparticles passing the 28 mesh standard screen should be kept to aminimum. Typical screen analysis follows:

`Table 3 Percent 0h 6 mesh 0.4 On 8 mesh 26.7 0n 10 mesh 26.3 On 20 mesh34.5 On 28 mesh f -3.2 On 35 mesh I 3.9 Thru 35 mesh 5.0

The finer sized chrome particles which pass the second screen are nowpassed over a third and tlner vibrating screen. All particles passingthrough this screen are set aside for subsequent use as iine chromeparticles. The particles which do not pass through the third screen arereground in a ball mill or similar fine grinding device and returned tothe third screen.

The size of the openings of the third screen is chosen so that; theproduct will pass substantially through W. S. Tyler standard screen ofor mesh per linear inch. Typical screen analysis follows:

I have found that this product can be readily produced in commercialquantities at lorir cost yand a product of this degree of lneness makesa satisfactory brick. However, for certain special uses and where theincreased cost is not objectionable the line chrome particles may bechosen to pass substantially all through a W. S. Tyler standard screenof 100 mesh or 150 mesh per linear inch or even 200 mesh or 250 mesh perlinear inch.

The dead-burned magnesite which is used may be prepared by calciningmagnesium hydroxide 'prepared from sea water as disclosed in my pendingU. S. patent application, Serial No. 411,695. Periclase or other typesof calcined or fused magnesia. are considered as materials equivalent todead-burned magnesite for the purposes of this disclosure. Typicalanalyses are the following: Table 5 Sea Water Magnesite Periclase Percent Per cmi Ignition Loss 0. l0 0.09 SiOs 1.2l 5.71 3.01 0.36 0.85 0.703.82 1.34 91.01 91.

Preferably the calcining should be done at temperatures of 1500 C. or1600 C. or more and the bulk specific gravity of the calcine shouldexceed 3.30. Dead-burned magnesite from other sources mayalso be used,as for example, the product obtained by calcining natural magnesite(magnesium carbonate), brucite or other suitable minerals. Typicalanalyses of such dead-burned magnesites are:

The magnesite is ground and screened to proper particle size using thegeneral procedure as outlined above. The size of the first, second andthird screens should be chosen in conformity with the principlesdescribed above. Coarse magnesite particles preferably passing through 6mesh and resting on 28 mesh Tyler standard screens areproduced. Othersizes such as passing through 8 mesh and resting on 28 mesh, or passing10 mesn and resting on 30 mesh, or other desired combinations forspecific purposes can be chosen. Fine magnesite particles passingthrough Tyler standard screens of or 65 mesh per linear inch areacceptable although for specific treating bauxite) or fused alumina mayalso be used.

I have secured excellent results with aluminous material comprising 50%or more of alumina on the calcined basis with the remainder chiey`silica and iron oxide, having a P. C. E. in excess of cone 33.

As an alternative small quantities of raw kaolin may also be required.This material may analyze as follows:

Table 10 Percent Loss on ignition 13.54 S102 42.64

. FeaOa 3.81 A1203 37.31 TiOz 1.48 CaO 0.09 MgO 0.71

It should be ground to pass substantially all through a Tyler standardscreen 200 mesh per linear-inch.

purposes particles passing screens of 100, 150,

200 or 250 mesh per linear inch may be chosen. A satisfactory screenanalysis of typical coarse and fine magnesite particles is thefollowing:

In addition to the chrome ore and magnesite it is quite desirable that asubstantial quantity of nelyground bauxite be incorporated into thebrick mix. A low silica bauxite such as that produced in Surinam issatisfactory. Typical chemical analysis is the following:

Table 9 Percent Loss on ignition 29.62 S102 4.54 FezOs 2.29 A1203 60.21TiOz 2.76 CaO 0.09 MgO 0.42

The bauxite is ground to pass substantially al1 through a Tyler standardscreen of 65 mesh per linear inch, or 100 mesh or finer, as desired. Rawbauxite is a satisfactory material although other high aluminousmaterials such as calcined alumina hydrate (prepared in the Bayerprocess for For making the brick, the above ingredients are mixed in thefollowing proportions by weight:

Table 11 Example #l Example #2 Per cent Per cent Coarse chrome particles30 30 Coarse Magnesite particles 35 35 Fine Chrome part1cles 10 10 FineMagnesite particles 23 Bauxte particles Kaolin Mixing is done in amuller-type wet pan. Preferably the muller and the pan bottom are rubbercovered to minimize the amount of grinding which may take place whilethe mixing is done.

Atemporary bond is added, such as a solution of sulphuric acid,magnesium chloride, magnesium sulphate, organic binders, etc. to givethe proper temper for pressing into brick form. The quantity of solutionadded should contain an amount of sulphuric acid equal to 1.1% by weightof the dry refractory. If desired sulphite liquor of 31 Baum about1.25%. by weight of the dry refractory may also be added to increase thestrength of the green brick before drying. The tempered brick mix shouldcontain about 4.5% Water.

'I'he brick are moulded into shape on a conventional dry press orpreferably on a hydraulic press. Pressures exceeding 5000 lbs. per sq.in. are desired and up to 10,000 lbs. per sq. inch or 15,000 lbs. persquare inch or more are preferred. By

A using a high forming pressure and properly chosen particle sizes abrick of low porosity is obtained.

After pressing, the brick are dried at 300 F. prefreably after apreliminary treatment in an atmosphere of high humidity as described inmy U. S. Patent No. 2,253,620. The dried brick are suitable for usewithout further treatment. 'I'hey have a crushing strength of 5,000lbs..per square inch or more and' can be transported for use s withoutdimculty. In fact, the brick are more suitable for use in the unburnedcondition than if subjected to a conventional kiln-burning at a.'temperature of 15007 C., for example. After such treatment the unburnedstrength is lost and the brick are changed over to the desired conditionof low modulus of rupture which is also a condition of low crushingstrength. The burned crushing strength is less than 1,500 lbs. per sq.inch v or less than 1,000 lbs. per sq. inch and brick of this lowstrength cannot always be transported without damage. Shipment in theunburned con-g dition avoids this diiliculty. When the unburned brickare placed in use, the heated portion of the brick is converted into thecondition of low strength whereupon it automatically becomes suitablefor use.

For best results the brick mix should contain 65% by weight of totalcoarse particles. This amount may be varied, however, within the limitsof 55% to 70%. The amount of intermediate particles should be kept totheminimum attainable with ordinary commercial grinding and screening.

The total amount of weight of magnesite in the brick should exceed thatof the chrome ore in order to give desirably low strength. The amount byweight of the chrome ore should not be less than 35% in order to avoidexcessive shrinkage upon firing to high temperatures. The amount of linechrome particles should lie between and 15%. If the amount of ne chromeis excessive .the brick will be attacked by iron oxide A with resultantbursting.

If the amount of fine chrome istoo small the brick will shrinkexcessively when fired to high temperature. If bauxite or similaralumina addition-s are made the amount by weight should lie between 1%and 10%. If calcined aluminous products are added a larger amount may beused than if raw bauxite is added.

When kaolin or similar alumino-silicates are used the amount by weightshould lie between 1% and 4%. After ming to 1500 C. the brick will havea total porosity less than 25%, a modulus of rupture, R., less than 500lbs. per sq. inch and a deformation, e, exceeding .0040" when tested asdescribed herein. Upon reheating to 1650 C. for 5 hours the brick willshow a, volume shrinkage of less than 1% or less than 0.5% as comparedto the original volume of the unburned brick. The brick are veryresistant to iron oxide attack.

These brick can be formed into the necessary shapes for constructingsuspended roofs and other mechanically supported sections ofmetallurgical furnaces, such as front-walls, back walls, monkey walls,end walls and downtakes of open hearth steel furnaces. For such usestheir unusually low strength provides increased resistance to spalling.Because of this low strength the brick are recommended for use incooperation with means for mechanical support or where such means is notprovided they should be used in parts of furnaces where higherstructural strength is not required.

An opening 21 is formed in the brick to receive a suspension hook 28.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent is:

1. A basic refractory brick in which dead burned .magnesite is the majorconstituent and chrome ore is present to an extent of at least 35%. therefractory of the brick consisting of a mixture of relatively coarseparticles between 5 and 35 mesh per linear inch present to 'the extentof 'between 55 and 70% and relatively fine particles below 50 mesh perlinear inch, substantially free from particles of intermediate size,inwhich between 20% and 40% of the mixture consists of relatively coarsedead burned magnesite particles and the modulus of rupture of therefractory body after an initial burning for twenty-four hours al? 1500C'. does not exceed 500 pounds per square inch when tested as a 9" x4*/2" x 21/2 brick acting as a beam 2*/2" thick supported at locations7' apart-and loaded at midspan.

2. A basic refractory brick in which dead burned magnesite is the majorconstituent and chrome ore is present to an extent of at least 3.5%, therefractory of the brick consisting of a mixture of relatively coarseparticles between 6 and 28 mesh per linear inch prescritto the extent ofbetween 55% and '70% and relatively ne particles below 50 mesh perlinear inch, substantially free from particles of intermediate size, inwhich between 20% and 40% of the mixture consists of relatively coarsedead burned magnesite particles and between 5% vand 15% of the mixtureconsists of relatively fine chrome ore particles and from 1% to 10% ofthe mixture consists of high aluminous material, and in which thedeflection of the refractory body exceeds 0.005" when tested for modulusof rupture after an initial burning for twenty-four hours at 1500 C.,using a 9" x 41/2" x 21/2" brick, acting as a beam 21/2" thick,supported at locations "I" apart and loaded at midspan.

3. Dry unred basic refractory brick suitable for used in unfiredcondition, in which dead burned magnesite is the major constituent andchrome ore is present to an extent of at least 35%, the refractory ofthe brick consisting of a mixture of relatively coarse particles between5 and 35 mesh per linear inch present to the extent of between 55% and70% and relatively fine particles below 50 mesh per linear inch,substantially free from particlesof intermediate size, and inpounds persquare inch when tested as a` 9 x 4%" x 21/2" brick acting as a beam2/2" thick supported at locations 7" apart loaded at midspan, the dryunred brick having a volume shrinkage of less than 1% after 5 hours at1650 C.

4. A dry unfired basic refractory brick, suitable for use in unfiredcondition. having head burned magnesite as the major constituent andchrome ore present to an extent of at least 35%, the refractoryof thebrick consisting of relatively' coarse particles between 6 and 28 meshper linear inch present to the extent of between 55% and 70% andrelatively ne particles below 50 mesh per linear inch, substantiallyfree' from particles of intermediate size, in which between 20% and 40%of the mixture consists of relatively coarse dead burned magnesiteparticles and between 5% and 15% of the mixture consists of relativelyfine chrome ore particles and the modulus of rupture of the refractorybody after an initial burning for 24 hours at 1500 C. does not exceed500 pounds per square inch when tested as a 9" x 41/2" x 21/2" brickacting as a beam 2%" thick, supported at, locations 7" apart and loadedat midspan, the dry uniired brick having a volume shrinkage of less than0.5% after 5 hours at burning 1650 C.

5. lA basic refractory brick having dead burned magnesite as the majorconstituent and chrome ore present to an extent of at least 35%, the re-13 per linear inch, substantially free from particles o! intermediatesize, in which between 20% and 40% of the mixture consists of relativelycoarse Y dead burned magnesite particles and between and 15% of themixture consists of relatively fine chrome ore particles and in whichthe deilection of the refractory body exceeds 0.005 when tested formodulus of rupture after an initial burning for 24 hours at 1500" C.using a 9" x 4l/2" X 217/2" brick acting as a beam 2%" thick supportedat locations 7" apart and loaded at midspan.

6. A dried unred basic refractory brick, suitable for use in uniiredcondition, having dead burned magnesite as the maior constituent andchrome ore is present to an extent of atleast 35%'. the refractory ofthe brick consisting of relatively coarse particles between 6 and 28mesh 9. The process of producing a. volume stable basic refractory brickhaving abnormally low modulus of rupture and corresponding highresistance to spa-lling in intermittent furnace sering through a 5 meshand resting upon a 35 mesh per linear inch screen, and relatively fineparticles passing through a 50 mesh per linear inch screen, whilesubstantially omitting particles of intermediate size, and havingbetween 20% and per linear inch present to the extent of substantially65% and relatively line particles below 50 mesh per linear inch,deiicient in particles of` intermediate size, in which substantially 35%of the mixture consists of relatively coarse dead burned magnesiteparticles, substantially 30% of relatively coarse chrome ore particles,substantially 2,0% of relatively fine dead burned magnesite particles,substantially 10% of relatively fine chrome orel particles andsubstantially 4% of bauxite, the refractory being densely compactedtogether, having a bonding agent, and having a -low modulus of ruptureafter an initial burning for twenty-four hours at l500 C. and lowcrushing strength when tested as a 9" x 41/2" x 21/2" brick acting as abeam 2%" thick supported at locations 7" apart and loaded at midspan,the dry unred brick having a volume shrinkage of less than one percentafter burning 5 hours at 1650 C.

7. An open hearth steel furnace suspendedv the deflection of therefractory body as outlined in claim 3 exceeds 0.005".

8. Dry unred basic refractory brick suitable for use in unred condition,in which dead burned magnesite is the major constituent and chrome oreis present to an extent of at least 35%, the

refractory of the brick consisting of relatively' coarse particlesbetween 5 and 35 mesh per linear inch present to the extent of between55% andk r10% and relatively fine particles below 50 mesh per linearinch, substantially free from particles of intermediate size, includingalso from 1% to 10% of iinely ground aluminous material, 'in whichbetween and 40% of the mixture consists of relatively coarse dead burnedmagnesite particles and the modulus of rupture of the refractory bodyafter an initial burning for twenty-four hours at 1500o C. does notexceed 400 pounds per square inch when tested as a 9" x 41/2" x 21/2"brick acting as a beam 241/2" thick supported at locations 'if' apartand loaded at midspan, the dry unilred brick having a volume shrinkageof less than 1% after 5 hours at 1650 C.

40% of relatively coarse dead burned magnesite in the mixture, and abonding agent, forming a mixture pressed into a, brick at a pressure ex.ceeding 5000 pounds per square inch, and drying the brick to develop thebond as the final operation without-flring prior to vfurnace use.

10. The process of protecting brick against spalling which consists informing the brick with a major constituent of dead burned magnesite andat least 35% of chrome ore, having between 55 and. 70% of relativelycoarse particlesbetween 5 and 35 mesh per linear inch and havingrelatively ne particles through 50 mesh per linear inch of each, lackingthe intermediate sizes, withv from 20% to 40% of the mixture ofrelatively coarse dead burned magnesite and a modulus of rupture below400 p. s. i. as determined after reheating a standard brick at 1500 C.for 24 hours and testing it under standard A. S. T. M. conditions oftest, the brick being unilred and having a higher unred crushingstrength than fired crushing strength after ve hours burning at 1650o C.and burning the exposed faces of the unred brick in place in a suspendedfurnace roof.

11. The process of producing a volume stable basic refractory brickhaving abnormally low modulus of rupture Aand corresponding highresistance to spalling in intermittent furnace service, which consistsin mixing together dead burned magnesite as a major constituent and atleast 35% of chrome ore in the form of from 55% to 70% ofrelativelycoarse particles passing through a 5 mesh and resting upon a35 mesh per linear inch screen, and relatively fine partic-les passingthrough a 50 mesh per linear inch screen while substantially omittingparticles vof intermediate size, and having between 20% and 40% ofrelatively coarse dead burned magnesite in the mixture, inserting from1% to 10% of a high aluminous material and tempering the mixture, and abonding agent, forming the mixture into a brick at a, pressure exceeding5000 pounds per square inch and drying the brick to develop the bond asthe nal operation without firing prior to furnace use.

12. The process of producing a volume stable basic refractory brickhaving abnormally low modulus of rupture and corresponding highresistance to spalling in intermittent furnace service, which consistsin mixing together dead burned magnesite as a major constituent and atleast 35% of chrome ore in the form of from 55% to 70% of relativelycoarse particles passing through a 5 mesh and resting upon a 35 mesh perlinear inch screen, and relatively flneparticles passing through a 50mesh per linear inch screen, lwhile substantially omitting particles ofintermediate size, and having between 20% and 40% of relatively coarsedead burned magnesite in the mixture, inserting from 1% to 10% ofbauxite and tempering the mixture, inserting a bonding agent, formingthe mixture into a brick l at a pressure exceeding 5000 pounds persquare inch and Vdryingr the brick to develop the bond as the fina-loperation without tiring prior to furnace use. l

13. The process of producing a volume stable basic refractory brickhaving abnormally low modulus of rupture and corresponding highresistancel to spelling in intermittent furnace service. which consistsin mixing together dead burned magnesite as a major constituent and atleast 35%A of chrome ore in the form of from 55% to 70% of relativelycoarse particles passing through a 5 mesh and resting upon a 35 mesh perlinear inch screen, and relatively ne particles passing through a 50mesh per linear inch screen, While substantially omitting particles ofintermediate size, and having between magnesite in the mixture,inserting from 1% to 'of kaolin and tempering the mixture, and insertinga bonding agent, forming the mixture into a brick at a pressureexceeding 5000 pounds per square inch and drying the brick tol developthe bond as the iinal operation without tiring prior to furnace use.

14. The process of forming and treating brick to provide basic roofbrick and protect them from spaliing, which consists in forming a greenbasic refractory brick by mixing dead burned magnesite as a majorconstituent and at least 35% of chrome ore as relatively coarseparticles between 5 and 35 mesh per linear inch to an extent -of between55 and 70% of which the majority are magneslte, and line particlesthrough 55 mesh per linear inch of which the maior-ity are also ofmagnesite, while substantially omitting the intermediate size ofparticles, employing to 40% of coarse particles of dead burnedmagnesite, thereby producing a dry uniired brick of relatively higher'modulus of rupture as compared with the iired brick so that advantageof this higher modulus of rupture can be taken at this point intransportation, suspending the brick from above and ring the exposedlower parts of the brick in use, whereby the up- 5 Yper'parts of thebrick remain unfired and re- `includingizhe adjacent parts within firingtemperature in the heat gradient from the exposed face of the brick, arered and their moduli o! rupture are reduced and their resistances tocompressive strain are reduced.

15. A basic refractory brick having provision for supporting it fromabove, containing dead burned magnesite as a major constituent and atleast 35% of chrome, comprising from 55 to 70% of relatively coarseparticles between 5 and 35 mesh per linear inch and relatively uneparticles below mesh per linear inch and substantially free fromparticles of intermediate sizes, in which from 20% to 40% of the mixtureis composed of relatively coarse magnesite particles, the modulus ofrupture after burning at 1500 C., as tested by A. S. T. M. Standardtests, is not more than 500 pounds per square inch and a maximumdeection of 0.0005" when tested for modulus of rupture, and the volumeshrinkage is less than 0.5% after ve hours burning at 1650* C.

16. A basic refractory brick mix comprising relatively coarse particlesbetween 5 and 35 mesh.

and relatively fine particles through 50 mesh per linear inch, andcomprising relatively' coarse chrome particles 30%, relatively coarsemagnesite particles 35%, relative fine magnesite particles 20%,relatively fine chrome particles 10%, and relatively fine bauxiteparticles 5%.

RUSSELL PEARC'E HEUER.

REFERENcEs CITED The following references are of record in the ille ofthis patent:

UNITED STATES PATENTS Number Name Date 1,394,470 Charles Oct. 18, 19211,644,166 Bainter Oct. 4, 1927 2,068,641 Carrie et al Jan. 26, 19372,079,066 Hartmann May 4, 1937 2,216,813 Goldschmidt Oct. 8, 19402,304,170 Heuer .l Dec. 8, 1942 FOREIGN PATENTS Number Country Date468,456 Great Britain 1937 664,044 Germany 1938 679,915 Germany 1939695,856 Germany 1940

